Session HB: Neutrino Physics II

CUORE: The Cryogenic Underground Observatory for Rare Events

CUORE is a next-generation double beta decay experiment designed primarily to search for the neutrinoless double beta decay of $^{130}$Te. CUORE will use a bolometric technique to measure the temperature changes produced in large crystals of TeO$_{2}$ when radiation is absorbed. $^{130}$Te was selected for initial study because of its high Q$_{\beta \beta }$ energy of 2529 keV and its large natural isotopic abundance of 34{\%}. These characteristics of $^{130}$Te place the expected position of the neutrinoless double beta decay peak above most background from terrestrial radioactive decays, and provide the desired experimental sensitivity without the need for expensive and time consuming isotopic enrichment. The construction of CUORE has recently begun at the LNGS in Italy. CUORICINO is a working prototype for CUORE and is currently the largest operating double beta decay experiment in the world. In this talk, the present status of CUORE and the latest experimental results from CUORICINO will be presented.   

Recent progress on the Majorana experiment

The Majorana collaboration proposes to search for the process of neutrinoless double-beta decay by employing high-purity, segmented, enriched (86\% $^{76}$Ge) germanium as both source and detector. Recent improvements in signal processing, detector design, and advances in controlling intrinsic and external backgrounds will augment this well-established technique. The Majorana reference design advances a scalable approach in which detectors are deployed in modules consisting of 57 1.1-kg germanium crystals in a cryostat made of electro-formed copper. The experiment's initial phase with one or more modules aims to quickly and definitively test a recent claimed observation of this decay in $^{76}$Ge by members of the Heidelberg-Moscow collaboration. In addition, the collaboration seeks to achieve backgrounds near 1 count/tonne/year in a 4 keV region-of-interest around the $^{76}$Ge double-beta decay endpoint (2039 keV) in order to demonstrate the required backgrounds for a next-generation experiment with $\ge$ 1 tonne detector mass. With such low backgrounds and after 3 years of running with 60 kg of 76Ge, Majorana will achieve a sensitivity of T$_{1/2}$ = $2 \times 10^{26}$ years (90\% CL), corresponding to a Majorana neutrino mass sensitivity of ~200 meV (using the latest RQRPA nuclear matrix element calculations\footnote{V.A. Rodin, {\it et al.}, nucl-th/0503063}).   

Neutron excitation of lead and copper in search for specific excited state decays

Monoenergetic neutron beams of 8 and 12 MeV were produced at the TUNL Shielded Neutron Source. The beam-on data obtained with three CLOVER detectors were used to measure the excitation function in lead and copper for some specific excited state decays. These decays are an important background for the next generation of double-beta decay experiments which are designed to reach the sensitivity set by the atmospheric neutrino mass scale. Measuring and understanding high energy neutron excitation of the shielding and detector materials for neutrinoless double beta decay experiments are crucial for interpreting the result and establishing the shielding requirements. Moreover, locating some specific excited state transitions, such as the 5/2$^{+}$ to 5/2$^{-}$ decay in $^{207}$Pb, the 1$^{-}$ to 1$^{+}$ decay in $^{206}$Pb etc., will make important contributions to nuclear structure.   

Prospects for Measuring Neutrino-Nucleus Coherent Scattering at a Stopped-Pion Neutrino Source

Coherent neutral current neutrino-nucleus elastic scattering has never been observed. Although the cross-section is very high, nuclear recoil energies are very small. However, detection of the process may be within the reach of the new generation of low-threshold detectors. A promising prospect for the first detection of this process is an experiment at a high flux stopped-pion neutrino source such as the SNS. Results of of some preliminary rate calculations will be presented, and sensitivity of such a measurement to new physics will be explored.   

Developing the Cosmic Ray Veto for $\nu$-SNS

The newly operational Spallation Neutron Source (SNS) will produce large quanities of neutrinos ($\sim2\times10^7 \nu/cm^2/s$ at 20m) at energies relevant to nuclear astrophysics. To exploit this opportunity, the proposed Neutrinos at the SNS ($\nu$-SNS) facility will host 2 detectors (target mass of $\sim$20 tons each) to measure neutrino-nucleus cross sections for a number of materials (e.g. C, O, Fe, Pb). Shielding the detectors from background is crucial so the facility will employ an iron bunker and a cosmic ray veto. As part of the $\nu$-SNS collaboration, the Colorado School of Mines nuclear group is responsible for the design and construction of this veto. Presented in this talk is the current progress for the research and development of the highly efficient, low cost, large veto panels based on extruded plastic scintillator.   

Three flavor neutrino oscillation analysis of atmospheric neutrinos in Super-Kamiokande

The nature of the neutrino mass hierarchy and the possibility of a nonzero $\theta_{13}$ are open problems in neutrino physics that can be probed by extending the standard two-flavor neutrino oscillation scenario to include all active flavors. In a three-flavor oscillation scheme there is known resonant enhancement (suppression) of the $\nu_{\mu} \rightarrow \nu_{e}$ transition probability in matter for several GeV neutrinos at long baselines for a normal (inverted) hierarchy when $\theta_{13} > 0 $. This effect is not present for the corresponding anti-neutrino transition. The Super-Kamiokande I atmospheric data has been analyzed using a three-flavor model testing both the normal and inverted mass hierarchies and has found no significant change in flux in its enriched multi-GeV $\nu_{\mu} $ or $\nu_{e}$ samples. Accordingly, confidence intervals for the atmospheric oscillation parameters have been obtained, the best fits being consistent with previous atmospheric results and zero $\theta_{13} $ for both hierarchies.   

NEXTEX- The next generation of electron anti-neutrino mass experiment

The design and progress towards meeting the objectives of the Neutrino Mass Experiment in Texas (NEXTEX) is presented. The mass of the electron antineutrino will be inferred from the beta endpoint energy spectrum from gaseous tritium molecules with precision of at least 0.5 eV. Two differential electrostatic spectrometers will be used to analyze the beta electrons near the endpoint energy with 1 eV resolution. The mass of the neutrino will be deduced following the deconvolution of the well established Fermi function and the measured spectrometer function. The correlations between electrodes' potentials and the energy of the transmitted electrons will be determined with high energy electron diffraction on the T$_{2}$ gas. The differential cross section exhibits an oscillatory pattern due to the coherent scattering from the two atoms forming T$_{2}$. This procedure will provide a series of calibration markers for the spectrum with uncertainties of about 100~meV. The background of less than one count a day, at the detector have been demonstrated. The isotopic purity of tritium is monitored by a novel, laser diode based Raman Spectrometer.   

Measuring the Neutrino Mixing Angle $\theta_{13}$ with Reactor Antineutrinos at Daya Bay

The observation of neutrino flavor change and mixing in recent experiments has provided compelling evidence for neutrino mass and oscillation. Two of the three neutrino mixing angles have been measured but the coupling of the electron neutrino flavor to the third mass eigenstate is not yet known. Its corresponding mixing angle $\theta_{13}$ is a fundamental paremeter of the new Standard Model and critical for future CP violation searches in the lepton sector. This talk will describe the proposed precision measurement of $\theta_{13}$ with the Daya Bay reactor antineutrino experiment and report on its recent progress and status. Using multiple liquid scintillator detectors at distances between 0.3 and 2~km from the Daya Bay-Ling Ao nuclear power plant the experiment plans to measure the subdominant $\overline{\nu}_{e}$ oscillation with a sensitivity of sin$^22\theta_{13} \le 0.01$.   

The Detector Calibration System for the Daya Bay Reactor Neutrino Experiment

The detector calibration system will be critical for the analysis of the Daya Bay Reactor Experiment. The experiment will use multiple detector modules at various baselines from the reactor cores to measure the neutrino mixing angle $\theta_{13}$ with a sensitivity to $\sin^2(2\theta_{13})<0.01$. The modules must be ``identical,'' therefore the detector properties need to be understood and calibrated accurately. In this talk, I will present some R\&D work towards an automated full-volume calibration system, including the simulation studies with various radioactive sources, as well as a preliminary hardware design.   

Development of Gadolinium-Loaded Liquid Scintillators for 1{\%}-Precision Measurement at the Daya Bay Nuclear Reactors of the Neutrino Mixing Angle, $\theta _{13}$

The Daya Bay collaboration intends to use multiple organic-liquid-scintillator (LS) detectors placed at various distances between 0.3 and 2 km from the Daya Bay-Ling Ao nuclear power reactors to detect antineutrino oscillations and to determine the unknown neutrino-mixing angle, $\theta _{13}$. The nuclear reaction in the LS is inverse $\beta $-decay on protons, with the coincidence tag between the emitted prompt positron and the delayed neutron-capture providing a clear signature of the antineutrino capture. The neutron-capture signal is enhanced by loading $\sim $0.1{\%} gadolinium into the liquid scintillator (Gd-LS), because of the 49000-barn (n,$\gamma )$ cross section of natural abundance Gd and the $\sim $8 MeV of emitted $\gamma $ rays. The Daya Bay plan is to use eight \textit{identical} antineutrino detectors, each containing 20 tons of Gd-LS. The BNL Nuclear Chemistry Group has developed chemical procedures to synthesize high-purity Gd-LS with long attenuation length ($>$15 m), high light output ($\sim $95{\%} of pseudocumene), and long-term stability ($>$1.5 years to date). Groups at IHEP in Beijing, China and JINR in Dubna, Russia are also doing Gd-LS R{\&}D. This paper discusses the properties of Gd-LS.